I've only been using this little ruler the most lately because of the number of paper piecing projects I've been doing - it's the "Add a Quarter" ruler. It has a little ridge on the bottom that snugs right up to the folded up paper to give you a good 1/4 " cut when trimming excess fabric. I know this is not a necessity, and may be considered extravagant, but it's come in very handy for the paperpiecing, and adding the quarter inch to some other patches I designed that needed the 1/4'" added.
Have fun shopping - you may end up with more than you planned - my problem when going on a trip and shopping for supplies or whatever - if I don't buy it when I see it, I'll dwell on it later wishing I had picked it up - then need to go back to get it later!